The devices on which drawers, trays and similar elements slide when pulled out from cabinets etc. are well known.
An intermediate, mobile, supporting runner ensures connection between a drawer, for example, and its place in a cabinet, part of the sliding device being fixed to the cabinet and part to the drawer.
When the drawer is being pulled out, the position of this mobile runner is given by the friction set up by small rollers and similar parts so that, because of the thrust received, of the loads, and of the materials used, sliding characteristics do not remain constant.
Further, since the runners are generally fixed at the side of the extractable part, due to the amount of force applied during the action, they frequently become deformed so that the drawer no longer slides smoothly and evenly.